Tracing prehistoric Pacific trades

10 March, 2010

Dr Nina Kononenko from the University of Sydney working with a portable digital microscope.Image: Catherine LovelockSource: Museum Victoria

Three researchers from the Australian Museum and the University of Sydney are using high-tech chemical analysis to track the origins of Museum Victoria’s obsidian artefacts. Combining the disciplines of anthropology, chemistry and geology, Dr Elizabeth Carter, Dr Robin Torrence and Dr Nina Kononenko are working to reconstruct how obsidian was traded by people in the Pacific region thousands of years ago.

In late February the visiting researchers examined Papua New Guinean obsidian tools and objects from the museum’s Pacific Collection. Obsidian is a natural volcanic glass formed when lava with high silicon content cools so quickly that it doesn’t form crystals. It can be fractured to create a very sharp edge, making it very useful for making cutting tools in prehistoric times.

The chemical composition of a piece of obsidian is like a characteristc ‘fingerprint’ of the volcano from which it came. Two analysis techniques were used to find these fingerprints: X-ray fluorescence spectroscopy (XRF), to identify kinds and quantities of elements such as iron and magnesium, and Raman spectroscopy, which identifies molecular structure. The unique chemical composition of each source of obsidian enables archaeologists to match tools found in archaeological sites back to the places where they were made. Changes in the way obsidian moved around the Pacific region provide important evidence about the nature of social interaction in ancient times.

Two islands in Papua New Guinea, New Britain and Manus, were sources of obsidian that was transported to other Pacific areas through trade or exchange, beginning about 20,000 years ago. Said Dr Torrence, “about 2,000 – 3,000 years ago, obsidian was being moved from sources in New Britain and Manus several thousand kilometres to Tonga, Fiji, and Samoa to the east and Borneo to the west.” During her visit, she studied examples of stemmed tools - a unique type of obsidian artefact made between about 10,000 and 3,400 years ago. Dr Kononenko also examined the blades for patterns of wear and deposits from previous use that would provide clues about their history.

XRF and Raman spectroscopy are invaluable tools to researchers because they produce immediate results and, unlike some other techniques, do not harm the objects in any way. Projects such as this one demonstrate that there’s often much to discover about objects in the museum’s collections.